In a protection scheme of a wavelength multiplexed OTN ring, when a failure occurs in a link, the failure is detected at the nodes of both ends of the failure link, and a switch message is transmitted in a reverse direction to a direction where the failure is detected. The switch message is a message for notifying each node of switching of a transmission direction of an optical signal. The switch message is prepared at the nodes of both ends of the failure link where the failure is detected, and has information of which a reception destination is the node of the other end of the failure link. A node in a halfway transfers the switch message, and the switch message finally arrives at the node of the other end of the failure link.
In a wavelength multiplexed ring network, the switch message is independently transmitted for each wavelength. However, when the number of wavelength-multiplexed wavelengths increases, the number of switch messages transmitted and received between the nodes increases, which increases the processing load at each node, and as a result, causes a delay in restoration from a failure.
Therefore, there is a technique that a plurality of wavelengths is made into one group and one switch message is transmitted in a group unit when the failure occurs in the link in the ring network. In this technique, when the failure occurs in one or more wavelengths in the group, one switch message is transmitted in the group unit, such that the transmission directions of optical signals of the respective wavelengths are integrated and switched at the node of the link end. As a result, as compared with the case in which the switch message is transmitted for each wavelength, the number of switch messages transmitted and received between the nodes may be decreased.
Related techniques are disclosed in, for example, Japanese Laid-Open Patent Publication No. 2013-030884, Japanese Laid-Open Patent Publication No. 2013-046269, and Japanese Laid-Open Patent Publication No. 2002-247038.